Elton T C Ngan

University of Nebraska at Lincoln, Lincoln, Nebraska, United States

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Publications (41)196.38 Total impact

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    ABSTRACT: Looking for an object that may be present in a cluttered visual display requires that an advanced specification of that object be created and then matched against the incoming visual input. Here, fast event-related fMRI was used to identify the brain networks that are active when preparing to search for a visual target. By isolating the preparation phase of the task it has been possible to show that for an identical stimulus, different patterns of cortical activation occur depending on whether participants anticipate a 'feature' or a 'conjunction' search task. When anticipating a conjunction search task, there was more robust activation in ventral occipital areas, new activity in the transverse occipital sulci and right posterior intraparietal sulcus. In addition, preparing for either type of search activated ventral striatum and lateral cerebellum. These results suggest that when participants anticipate a demanding search task, they develop a different advanced representation of a visually identical target stimulus compared to when they anticipate a non demanding search.
    Brain research 07/2013; · 2.46 Impact Factor
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    ABSTRACT: Dual-stream modulation failure (DSMF) proposes that dysfunctional regulation of logical and intuitive decision-making processes by conflict and emotional salience may be the underlying cognitive mechanism for the formation and maintenance of delusions in schizophrenia. The present study utilizes a combination of emotionally salient and neutral stimuli in conflict and non-conflict conditions in a sentence verification task to test specific hypotheses predicted by the model. Twenty-one patients with schizophrenia and 21 controls completed a sentence verification task with fMRI acquisition. The results are consistent with the predictions based on the conflict modulation component of the model, but do not support the emotional modulation component of the model.
    Frontiers in Psychiatry 01/2013; 4:113.
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    ABSTRACT: In this follow-up study, self-referential videos of success and failure were used for mood provocation to investigate mood, neural, and endocrine activity among 26 internationally competitive athletes using functional Magnetic Resonance Imaging (fMRI) and salivary hormone measures. The initial sample of 14 athletes who had experienced career-threatening failure was contrasted to 12 athletes with exceptional success. Endocrine data were added to the preliminary report to round out a psychoneuroendocrinology perspective on success and failure. On-line and prepost mood ratings confirmed successful mood provocation. fMRI BOLD signals revealed significantly greater activation in right premotor cortex and left sensorimotor cortices following self-reference video for successful athletes than (previously reported) failed athletes. Percentage gains in the ratio of testosterone to cortisol from Time 1 to Time 2 among success athletes positively correlated with right premotor cortex BOLD activity. Overall, the results suggest that affect associated with self-reference corresponds to an integrated neural and endocrine response to competitive challenge.
    03/2012;
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    ABSTRACT: Constrained principal component analysis (CPCA) with a finite impulse response (FIR) basis set was used to reveal functionally connected networks and their temporal progression over a multistage verbal working memory trial in which memory load was varied. Four components were extracted, and all showed statistically significant sensitivity to the memory load manipulation. Additionally, two of the four components sustained this peak activity, both for approximately 3 s (Components 1 and 4). The functional networks that showed sustained activity were characterized by increased activations in the dorsal anterior cingulate cortex, right dorsolateral prefrontal cortex, and left supramarginal gyrus, and decreased activations in the primary auditory cortex and "default network" regions. The functional networks that did not show sustained activity were instead dominated by increased activation in occipital cortex, dorsal anterior cingulate cortex, sensori-motor cortical regions, and superior parietal cortex. The response shapes suggest that although all four components appear to be invoked at encoding, the two sustained-peak components are likely to be additionally involved in the delay period. Our investigation provides a unique view of the contributions made by a network of brain regions over the course of a multiple-stage working memory trial.
    Human Brain Mapping 06/2011; 32(6):856-71. · 6.88 Impact Factor
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    ABSTRACT: Working memory (WM) is one of the most impaired cognitive processes in schizophrenia. Functional magnetic resonance imaging (fMRI) studies in this area have typically found a reduction in information processing efficiency but have focused on the dorsolateral prefrontal cortex. In the current study using the Sternberg Item Recognition Test, we consider networks of regions supporting WM and measure the activation of functionally connected neural networks over different WM load conditions. We used constrained principal component analysis with a finite impulse response basis set to compare the estimated hemodynamic response associated with different WM load condition for 15 healthy control subjects and 15 schizophrenia patients. Three components emerged, reflecting activated (task-positive) and deactivated (task-negative or default-mode) neural networks. Two of the components (with both task-positive and task-negative aspects) were load dependent, were involved in encoding and delay phases (one exclusively encoding and the other both encoding and delay), and both showed evidence for decreased efficiency in patients. The results suggest that WM capacity is reached sooner for schizophrenia patients as the overt levels of WM load increase, to the point that further increases in overt memory load do not increase fMRI activation, and lead to performance impairments. These results are consistent with an account holding that patients show reduced efficiency in task-positive and task-negative networks during WM and also partially support the shifted inverted-U-shaped curve theory of the relationship between WM load and fMRI activation in schizophrenia.
    Schizophrenia Bulletin 01/2011; 38(4):803-13. · 8.80 Impact Factor
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    ABSTRACT: Dual-stream information processing proposes that reasoning is composed of two interacting processes: a fast, intuitive system (Stream 1) and a slower, more logical process (Stream 2). In non-patient controls, divergence of these streams may result in the experience of conflict, modulating decision-making towards Stream 2, and initiating a more thorough examination of the available evidence. In delusional schizophrenia patients, a failure of conflict to modulate decision-making towards Stream 2 may reduce the influence of contradictory evidence, resulting in a failure to correct erroneous beliefs. Delusional schizophrenia patients and non-patient controls completed a deductive reasoning task requiring logical validity judgments of two-part conditional statements. Half of the statements were characterized by a conflict between logical validity (Stream 2) and content believability (Stream 1). Patients were significantly worse than controls in determining the logical validity of both conflict and non-conflict conditional statements. This between groups difference was significantly greater for the conflict condition. The results are consistent with the hypothesis that delusional schizophrenia patients fail to use conflict to modulate towards Stream 2 when the two streams of reasoning arrive at incompatible judgments. This finding provides encouraging preliminary support for the Dual-Stream Modulation Failure model of delusion formation and maintenance.
    European Psychiatry 09/2009; 25(2):80-6. · 3.29 Impact Factor
  • NeuroImage 01/2009; 47. · 6.25 Impact Factor
  • Steven Brown, Elton Ngan, Mario Liotti
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    ABSTRACT: The map of the human motor cortex has lacked a representation for the intrinsic musculature of the larynx ever since the electrical stimulation studies of Penfield. In addition, there has been no attempt to localize this area using neuroimaging techniques. Because of the central importance of laryngeal function to vocalization, we sought to localize an area controlling the intrinsic muscles of the larynx by using functional magnetic resonance imaging and to place this area in a somatotopic context. We had subjects perform a series of oral tasks designed to isolate elementary components of phonation and articulation, including vocalization of a vowel, lip movement, and tongue movement. In addition, and for the first time in a neuroimaging study, we had subjects perform "glottal stops," in other words forced closure of the glottis in the absence of vocalizing. The results demonstrated a larynx-specific area in the motor cortex that is activated comparably by vocal and nonvocal laryngeal tasks. Converging evidence suggests that this area is the principal vocal center of the human motor cortex. Finally, the location of this larynx area is strikingly different from that reported in the monkey. We discuss the implications of this observation for the evolution of vocal communication in humans.
    Cerebral Cortex 05/2008; 18(4):837-45. · 6.83 Impact Factor
  • Sara Weinstein, Rachel McKay, Elton T Ngan
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    ABSTRACT: This study examined whether speech abnormalities typical of formal thought disorder in schizophrenia vary with the degree of positive schizotypy in the healthy population. We hypothesized that participants with high levels of positive schizotypy would show greater abnormality in speech relative to those with low levels of positive schizotypy. Participants (n=107) were prescreened with a positive schizotypy scale. Those meeting criteria for either high (n=23) or low (n=27) schizotypy provided speech samples which were assessed with a clinical though disorder rating scale (Thought and Language Index) for the presence of abnormality. No significant differences were found in positive (P=0.25) or negative (P=0.21) speech abnormality between the high and low schizotypy groups. Although schizotypy is normally distributed in the general population, speech abnormality is not. Thus, the presence of aberrations in speech may predict risk of psychosis. Potential implications for risk assessment are discussed.
    Early Intervention in Psychiatry 05/2008; 2(2):98-102. · 1.65 Impact Factor
  • William J Speechley, Elton T C Ngan
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    ABSTRACT: Delusions, a cardinal feature of schizophrenia, are characterized by the development and preservation of false beliefs despite reason and evidence to the contrary. A number of cognitive models have made important contributions to our understanding of delusions, though it remains unclear which core cognitive processes are malfunctioning to enable individuals with delusions to form and maintain erroneous beliefs. We propose a modified dual-stream processing model that provides a viable and testable mechanism that can account for this debilitating symptom. Dual-stream models divide decision-making into two streams: a fast, intuitive and automatic form of processing (Stream 1); and a slower, conscious and deliberative process (Stream 2). Our novel model proposes two key influences on the way these streams interact in everyday decision-making: conflict and emotion. Conflict: in most decision-making scenarios one obvious answer presents itself and the two streams converge onto the same conclusion. However, in instances where there are competing alternative possibilities, an individual often experiences dissonance, or a sense of conflict. The detection of this conflict biases processing towards the more deliberative Stream 2. Emotion: highly emotional states can result in behavior that is reflexive and action-oriented. This may be due to the power of emotionally valenced stimuli to bias reasoning towards Stream 1. We propose that in schizophrenia, an abnormal response to these two influences results in a pathological schism between Stream 1 and Stream 2, enabling erroneous intuitive explanations to coexist with contrary logical explanations of the same event. Specifically, we suggest that delusions are the result of a failure to reconcile the two streams due to both a failure of conflict to bias decision-making towards Stream 2 and an accentuated emotional bias towards Stream 1.
    Medical Hypotheses 02/2008; 70(6):1210-4. · 1.18 Impact Factor
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    ABSTRACT: Athletes who fail are susceptible to negative affect (NA) and impaired future performance. Functional magnetic resonance imaging (fMRI) studies have identified prefrontal, anterior cingulate, and limbic activations following negative mood provocation. Little is known about the neural correlates of negative self-reference (SR), especially in athletes. Even less is known about the neural correlates of the effects of cognitive intervention (CI) in modifying negative SR and NA in this population. In an fMRI study, 13 athletes watched a video of their own career-threatening defeat in two controlled blocks. Between fMRI blocks, they received a 20-min CI designed to assist in event reappraisal and planning for future performance. Relative increases post-CI were seen in premotor (BA6) and sensorimotor (BA4/1) cortices. Correlated with mood ratings, relatively higher pre-CI levels were seen in the ventromedial prefrontal cortex, the right dorsomedial prefrontal cortex (PFC; BA10), the right dorsolateral PFC (BA45), the anterior cingulate, and the right parahippocampus. CI may counteract the detrimental effects of NA and negative SR on premotor and motor activity.
    Brain Imaging and Behavior 01/2008; 2(2):84-93. · 2.67 Impact Factor
  • Schizophrenia Research - SCHIZOPHR RES. 01/2008; 102(1):132-132.
  • Schizophrenia Research - SCHIZOPHR RES. 01/2008; 102(1):96-96.
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    Sara Weinstein, Todd S Woodward, Elton T C Ngan
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    ABSTRACT: Thought disorder is a symptom of schizophrenia expressed as disorganized or incoherent speech. Severity of thought disorder correlates with decreased left superior temporal gyrus grey matter volume and cortical activation in posterior temporal regions during the performance of language tasks. The goal of this study was to determine whether language-related activation mediates the association between thought disorder and left superior temporal lobe grey matter volume. 12 patients with schizophrenia were assessed for thought disorder. FMRI images were acquired for each subject while they listened to English speech, along with a high resolution structural image. Thought disorder was used as a covariate in the functional analysis to identify brain regions within which activation correlated with symptom severity. Voxel based morphometry was used to calculate grey matter volume of the planum temporale. A mediation model waste-tested using a four-step multiple regression approach incorporating cortical volume, functional activation and symptom severity. Thought disorder correlated with activation in a single cluster within the left posterior middle temporal gyrus during listening to speech. Grey matter volume within the planum temporale correlated significantly with severity of thought disorder and activation within the functional cluster. Regressing thought disorder on grey matter volume and BOLD response simultaneously led to a significant reduction in the correlation between grey matter volume and thought disorder. These results support the hypothesis that the association between decreased grey matter volume in the left planum temporale and severity of thought disorder is mediated by activation in the posterior temporal lobe during language processing.
    NeuroImage 05/2007; 36(1):188-93. · 6.25 Impact Factor
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    ABSTRACT: Thought disorder is a fundamental symptom of schizophrenia, observable as irregularities in speech. It has been associated with functional and structural abnormalities in brain regions involved in language processing, including left temporal regions, during language production tasks. We were interested in the neural correlates of thought disorder during receptive language processing, as this function is relatively preserved despite relying on the same brain regions as expressive language. Twelve patients with schizophrenia and 11 controls listened to 30-s speech samples while undergoing fMRI scanning. Thought disorder and global symptom ratings were obtained for each patient. Thought disorder but not global symptomatology correlated positively with the BOLD response in the left posterior superior temporal lobe while listening to comprehensible speech (cluster-level corrected p=.023). The pattern of brain activity associated with thought disorder during listening to comprehensible speech differs from that seen during language generation tasks, where a reduction of the leftward laterality of language has often been observed. As receptive language is spared in thought disorder, we propose that the increase in activation reflects compensatory processing allowing for normal performance.
    Schizophrenia Research 10/2006; 86(1-3):130-7. · 4.59 Impact Factor
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    ABSTRACT: Patients with schizophrenia have an impaired ability to generate activity that is appropriate to current circumstances and goals. We report a study using functional magnetic resonance imaging (fMRI) to examine cerebral activity during a three-tone auditory oddball target detection task in a sample of 28 patients with schizophrenia and 28 healthy controls. The patients exhibited significantly less activation in response to target stimuli relative to baseline in an extensive set of sites in association neocortex, paralimbic cortex, limbic structures and subcortical nuclei, yet demonstrated a normal level of activation in the sensorimotor cortex. Comparison of activity elicited by rare target stimuli with that elicited by equally rare novel stimuli makes it possible to distinguish cerebral activity associated with attention to behaviourally salient stimuli from activity associated with attending to other attention-capturing stimuli. This comparison revealed that the patients with schizophrenia also exhibited a deficit in activation of basal forebrain areas that mediate motivation during the processing of behaviourally salient stimuli, including the amygdala, ventral striatum, orbital frontal cortex and rostral anterior cingulate cortex. Patients with schizophrenia have a deficit in function of the brain system concerned with mediating motivation, in addition to a more general deficit in the cerebral response to attention-captivating stimuli.
    Psychological Medicine 09/2006; 36(8):1097-108. · 5.59 Impact Factor
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    Tara A Cairo, Todd S Woodward, Elton T C Ngan
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    ABSTRACT: Working memory deficits are a cardinal feature of schizophrenia that contribute to social and occupational dysfunction. We used functional magnetic resonance imaging to compare the response to varying task demands during the performance of an item recognition task. Study design and analysis procedures were optimized for the detection of load dependent activity during the encoding phase of working memory. At the lowest load conditions the schizophrenia group performed as well as controls, however to achieve this equivalent performance the schizophrenia group had a significantly higher magnitude of activation compared to the controls. At the higher load conditions, the magnitude of activation between groups became more similar and we began to see performance deficits in the schizophrenic group. These results suggest that patients with schizophrenia have decreased efficiency in the cognitive processes that underlie the early encoding phase of this task. For lower demand tasks, patients with schizophrenia can compensate for decreased efficiency by working harder to achieve equivalent performance. Encoding utilizes attentional and perceptual cognitive operations that are likely common to many other cognitive tasks; therefore, inefficiency may underlie the deficits observed in a wide range of cognitive tasks in schizophrenia compared to healthy controls.
    Biological Psychiatry 05/2006; 59(8):740-6. · 9.25 Impact Factor
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    ABSTRACT: One of the main challenges in working memory research has been to understand the degree of separation and overlap between the neural systems involved in encoding and maintenance. In the current study we used a variable load version of the Sternberg item recognition test (two, four, six, or eight letters) and a functional connectivity method based on constrained principal component analysis to extract load-dependent neural systems underlying encoding and maintenance, and to characterize their anatomical overlap and functional interaction. Based on the pattern of functional connectivity, constrained principal component analysis identified a load-dependent encoding system comprising bilateral occipital (Brodmann's area (BA) 17, 18), bilateral superior parietal (BA 7), bilateral dorsolateral prefrontal (BA 46), and dorsal anterior cingulate (BA 24, 32) regions. For maintenance, in contrast, constrained principal component analysis identified a system that was characterized by both load-dependent increases and decreases in activation. The structures in this system jointly activated by maintenance load involved left posterior parietal (BA 40), left inferior prefrontal (BA 44), left premotor and supplementary motor areas (BA 6), and dorsal cingulate regions (BA 24, 32), while the regions displaying maintenance-load-dependent activity decreases involved bilateral occipital (BA 17, 18), posterior cingulate (BA 23) and rostral anterior cingulate/orbitofrontal (BA 10, 11, 32) regions. The correlation between the encoding and maintenance systems was strong and negative (Pearson's r = -.55), indicting that some regions important for visual processing during encoding displayed reduced activity during maintenance, while subvocal rehearsal and phonological storage regions important for maintenance showed a reduction in activity during encoding. In summary, our analyses suggest that separable and complementary subsystems underlie encoding and maintenance in verbal working memory, and they demonstrate how constrained principal component analysis can be employed to characterize neuronal systems and their functional contributions to higher-level cognition.
    Neuroscience 05/2006; 139(1):317-25. · 3.12 Impact Factor
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    ABSTRACT: Alternating between task sets involves detection that the current task set is unfavorable, initiation of a change in set, and application of the new task set while fine-tuning to optimally adjust to the demands of the environment. Functional magnetic resonance imaging (fMRI) studies of cognitive flexibility consistently report activation of the anterior cingulate cortex and/or adjacent pre-supplementary motor regions (ACC/pre-SMA, medial Brodmann's areas 24/32/6), suggesting that these cortical regions are involved in switching task set. In the current study, our objective was to probe whether ACC/pre-SMA activation would decrease for a number of trials following a switch in task set, implying longer-term involvement in fine-tuning adjustments. By measuring activation when switching between word reading and color naming in response to Stroop stimuli, ACC/pre-SMA activation was observed when actively countering the influence of the irrelevant task set, and this activation decreased as a function of the number of trials since a task switch. Basal ganglia and thalamic regions also displayed a decreased response over successive trials after task switches. These findings suggest that the ACC/pre-SMA are not only involved in generating a new course of action, but are also involved (along with subcortical regions) in fine-tuning operations that resolve competition between task sets over subsequent repetitions of the same task.
    Brain Research 02/2006; 1068(1):161-9. · 2.88 Impact Factor
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    ABSTRACT: Relational association of disparate semantic concepts can strengthen encoding of episodes. Previous research has shown that the left medial temporal lobe (MTL) and the left prefrontal cortex (PFC) are the primary brain regions activated during both verbal encoding and the association of disparate semantic concepts. In the current functional magnetic resonance imaging (fMRI) study, our goal was to compare the coordinated response of the left MTL and left PFC when disparate semantic associations are strongly encoded compared to when they are weakly encoded. To achieve this goal, subjects were scanned while creating sentences based on a presented pair of words, and were asked to free-recall these sentences at a later time. Half the word pairs were semantically unrelated, and half were semantically related. Analysis of relatedness activations (unrelated-related contrast) suggested that the PFC was active whether or not the items were free-recalled, and increased activation of the MTL was required to promote encoding. Analyses of coordination of relatedness activations comparing free-recalled items to not free-recalled items showed an increase in left MTL-left PFC coordination for relatedness activations on free-recalled items. These results suggest that formation of relational semantic associations that lead to strongly encoded episodes requires increased coordination of the left MTL-left PFC neural pathway.
    Neuropsychologia 02/2006; 44(12):2308-14. · 3.48 Impact Factor

Publication Stats

1k Citations
196.38 Total Impact Points

Institutions

  • 2013
    • University of Nebraska at Lincoln
      Lincoln, Nebraska, United States
  • 2000–2013
    • University of British Columbia - Vancouver
      • • Department of Psychiatry
      • • Department of Psychology
      Vancouver, British Columbia, Canada
  • 2008
    • Simon Fraser University
      • Department of Psychology
      Burnaby, British Columbia, Canada
  • 2005
    • King's College London
      • Institute of Psychiatry
      London, ENG, United Kingdom
  • 2004
    • Université de Montréal
      • Department of Psychiatry
      Montréal, Quebec, Canada